April 11 (Reuters) - Whitehaven Coal Ltd on Thursday lowered its production guidance for fiscal 2019 after a decline in saleable coal output for the March quarter, hurt by lower yields from its Maules Creek Mine in New South Wales.

Whitehaven, which mines thermal and metallurgical coal from six mines in New South Wales state, said managed saleable coal production fell 3 percent to 5.06 million tonnes in the three months to March 31.

The company lowered its 2019 production guidance for saleable coal to 20.5 million tonnes to 21 million tonnes on a managed basis, from the prior range of 21.5 million tonnes to 22.5 million tonnes.

Whitehaven plans to increase its output of higher-grade coal to benefit from higher prices compared with other grades, because the higher quality fuel is less polluting.

Whitehaven is among the top producers of high-quality coal for the Asian market, with the governments of Japan and Korea key customers.

“Costs continued to moderate through the second half and, with the prospect of in-pit dumping at Maules Creek starting in FY2020, we are passing the peak of costs at our largest operation,” said CEO and Managing Director Paul Flynn.

Whitehaven said it produced 4.9 million tonnes of total run-of-mine coal in the March quarter, down 17 percent from a year earlier.